Abstract: Aiming at the problem that the influence of gangue particle size on the rheological properties of slurry in the process of fluidized filling is not clear, this study systematically reveals the mechanism of gangue particle size on the rheological properties of slurry and the mechanical behavior of gangue particles in the process of pipeline transportation by carrying out the rheological properties test of gangue fluidized filling materials with different particle size gradations. The results show that: under the specific particle size distribution, the gangue fluidized filling slurry shows Bingham plastic flow characteristics, and by comparing the maximum Reynolds number with the critical Reynolds number, it is determined that the slurry is laminar flow in the pipeline transportation process. The stress analysis of gangue particles in slurry shows that the force to promote the settlement of gangue is positively correlated with the third power of particle size, while the force to prevent the settlement of gangue is positively correlated with the second power of particle size. Based on ANSYS FLUENT numerical simulation, the influence laws of different gangue particle sizes on pipeline transportation speed and resistance loss are revealed. Combined with the experimental and simulation results, it is proposed that the maximum particle size of gangue aggregate of fluidized filling slurry should be controlled below 3 mm. This study has important guiding significance for optimizing the proportion design of gangue fluidized filling slurry and its practical application in coal mine filling engineering.